It is known that an optical fiber cable comprises one or more transmission or telecommunication elements, each one of which is constituted by one or more optical fibers and has one or more protective layers or sheaths, generally made of plastic material. The assembly of said elements usually is protected by suitable materials among which are, preferably, but not exclusively, plastic materials.
It is known that articles manufactured from plastic materials are susceptible to variations in their dimensions because of the discharging of mechanical stresses that are created therein during the course of the working processes.
Moreover, it is also known that the coefficient of thermal expansion of the plastic materials is high and significantly greater than that of metals.
It is equally known that optical fibers are very sensitive to deformations that, even if of a small size, cause increases in the attenuation of the light transmitted therethrough.
For preventing the fiber from being affected by the dimensional variations in said plastic materials, attempts have been made to offset the dimensional variations in said plastic materials by introducing into the optical fiber cable elements which are made of more stable materials, e.g. having both a low coefficient of thermal expansion, as well as a high elastic modulus.
Thus, there have been made optical fiber cables comprising one or more fibers, clad with plastic materials that are joined or wound on an inner longitudinal metallic element, for example, on a steel wire.
However, although this solution is effective from the point of view of dimensional stability, it presents other drawbacks during practice.
Take, for example, a buried cable. In case of an electrical discharge caused by a flash of lightning striking the ground, said discharge can reach the inner metallic element with damage to the fibers that it encounters during the course of discharging itself.
Discharges could also be caused by variations in the electromagnetic field resulting, for example, from transient short circuits in the power transmission lines that are adjacent to an optical fiber.